Hypertension in youth is no longer a rare disease and the number of affected children and adolescents is growing with the evolving pediatric obesity epidemic in the US. Hypertension tracks from adolescence into adulthood and has been linked with preclinical indicators of adverse cardiovascular events in adults. Early prevention and intervention efforts are needed to address this increasing public and individual health problem. Preliminary studies from our research group demonstrate promising short-term effects of a behavioral nutrition intervention emphasizing a diet high in fruits, vegetables, and low fat dairy that is also low in fat and sodium (the DASH diet) on lowering blood pressure (BP) in adolescents. The purpose of this application is to extend these findings by examining the long term effects of an improved 24-week clinically-based behavioral nutrition intervention emphasizing the DASH diet (the DASH-4-Teens intervention) compared to routine nutrition care intervention on changing diet quality, BP, hypertension status, and vascular function in adolescents with elevated BP. The primary objectives of this study are two-fold: 1) to determine the impact of the intervention on dietary intake, BP, hypertension status, and vascular function immediately post-treatment and at 1 year follow-up, and 2) to examine the relationship between intervention adherence and diet, BP and vascular outcomes. Adolescents with diagnosed pre-hypertension and stage 1 hypertension will be randomly assigned to receive either the DASH-4-Teens intervention or routine nutrition care. The DASH-4-Teens intervention will include individual in-person nutrition counseling sessions, behavioral counseling telephone calls, and mailings. Routine nutrition care will include individual in-person counseling sessions on guidelines consistent with the Fourth Pediatric Report of the National High Blood Pressure Education Program. Primary outcomes will be measured in both conditions at 6 months (post-treatment) and at 1 year follow-up. Adherence to treatment will be measured as diet-related goals met, counseling session attendance, and telephone call and food monitoring completion. Findings are expected to improve the treatment of hypertensive adolescents in the clinical setting and contribute to the enhancement of the cardiovascular health of this population. Narrative: Hypertension can have deleterious effects on the cardiac and vascular systems in youth, yet there is a lack of proven effective treatment strategies for managing high blood pressure and restoring impaired cardiovascular function in early life. Strides in developing effective and generalizable treatment protocols for pediatric hypertension are urgently needed. A positive outcome from this clinical trial could have profound implications for future research and treatment recommendations for early intervention in managing primary hypertension.